The central neurochemistry service has provided routine analysis for MHPG, HVA, 5HIAA, 5HT, NE and normetanephrine in plasma. These compounds as well as VMA, DOPAC, epinephrine, dopamine, metanephrine, and 3- methoxytyramine can be measured in urine. In addition, CSF measures of epinephrine, NE, DA, HVA, 5HIAA, MHPG, free and conjugated metanephrine and normetanephrine, and 5HT are possible. Both HPLC with electrochemical detection and GCMS are utilized for quantification. Cumulatively, over 5,000 analyses were provided during the last twelve months. Further, development of microdialysis methods to interpret what contributes to the overall "extracellular" concentrations in brain of a variety of substances including cyclic AMP derives from application of a theoretical model developed in the Biomedical Engineering Program of the National Center for Research Resources. Diffusion profiles around the probe are being determined for major solutes of interest so that the area which microdialysis samples can be accurately specified. This advance is essential to regional brain studies with in vivo microdialysis.